Interventional radiology procedures are becoming increasingly important in the treatment of physiological abnormalities such as lumen stenosis or aneurysm. For example, in order to treat a stenotic coronary artery, it is often required to inflate a balloon, apply an atherectomy or thrombectomy device and place a stent (prosthesis) at a diseased artery site. The intravascular device (balloon, stent, atherectomy or thrombectomy device, for example) is usually mounted onto a guide wire and brought to the vessel to be treated using the guide wire and a catheter. When the catheter tip has reached the arterial region to be treated, the guide wire is extended from the catheter tip and is used to position the device inside the artery. Once the device is positioned within the artery and deployed, repositioning of the device is either impossible or may significantly increase the risk of injury to the artery and can result in total blockage to the treated artery.
Accurate positioning of the intravascular device at a specific site within an artery is essential for successful treatment. Improper positioning of a stent at the diseased site within the artery, or use of a longer stent than is actually required in order to compensate for inaccurate positioning, may significantly increase the chance for subsequent renarrowing of the artery. Moreover, in atherectomy procedures, inaccurate positioning and deployment of the device in the artery may cause a fatal thrombosis. Therefore, accurate determination of the location of an intravascular device in an artery is vital during any interventional therapeutic procedure.
The location of a catheter tip or intravascular device with reference to surrounding arterial anatomy is monitored by X-ray fluoroscopy. An angiographer releases a contrast material, such as iodine solution, from the catheter tip. The contrast material is carried from the catheter tip by the blood flow, and an X-ray image of the arterial anatomy in the vicinity of the catheter tip is obtained. Based upon the obtained X-ray image, the catheter is advanced until the desired arterial anatomy is reached. Then, the guide wire is extended from the catheter tip and brought to the diseased artery using fluoroscopy and short injections of contrast material. Usually, in order to treat the artery, the tip of the guide wire should pass through the diseased region to the distal end of the diseased region. Subsequently, an intravascular device is extended over the guide wire and brought to the diseased arterial region. Monitoring the location of the device inside the artery is performed by following the movement of two radio-opaque markers slidable along the guide wire that flank the device. The markers indicate the position of the device in reference to the guide wire in conjunction with short injections of contrast material. Typically, prior art methods require that the device be introduced stepwise into the organ and at each step the device and organ imaged so as to show the instantaneous position of the device relative to the organ. This is repeated as required until the device is positioned at the desired location. Such an approach requires that a contrast material be released into the organ in order for the organ to be imaged together with the device. Since many images may be required, the total amount of contrast material released into the blood may be quite large and harmful to the patient. Moreover, determining the location of the device in an artery in relation to the region to be treated is often inaccurate by this method. The main reason for this may be attributed to the fact that assessment of the morphology and length of disease in the artery is strongly dependent on the perspective from which the artery is viewed.
WO 96/25881 entitled “Method for ultrasound guidance during clinical procedures” published Aug. 29, 1996 describes a method using external ultrasound modality to derive angiography 3D reconstruction. External ultrasound modality cannot be applied for some organs, such as coronary arteries, which are an important implementation field for our invention.
Essentially, this reference describes a method for guiding a tool to reach an organ without intersecting other organs. It does not relate to navigation of a tool located inside a tubular organ to a pre-defined position within the tubular organ.
WO 01/58359 entitled “Ultrasonic Images” was published Aug. 16, 2001 i.e. after the international filing date of the present application and discloses an ultrasound imaging system that superimposes sectional views created from volumetric ultrasound data and the location data for an intervention device, such as a catheter. The position of an interventional medical device may be shown, in one or more views, relative to organs and tissues within a body as the interventional device is moved. The interventional device positional data is updated continuously and is superimposed on tissue images that may be updated less frequently, resulting in real-time or near real-time images of the interventional device relative to the tissues. The superimposed images permits medical personnel to perform procedures such as angiograms with minimal or no exposures of patients to x-rays and contrasting dye.
WO 99/13432 entitled “Apparatus and method for determining three-dimensional representations of tortuous vessels ” published Mar. 18, 1999 discloses a method for three dimensional reconstruction of vessels. It does not teach how to use such a method to navigate a tool located side a tubular organ to a pre-defined position within the tubular organ.
It would therefore be desirable to provide a method and system for navigating a tool located inside a tubular organ to a predefined position within the tubular organ. It would be particularly advantageous to provide such a method and system where re-imaging of the organ for each incremental advance of the device in the organ is avoided.